Long-Term Evolution (LTE) is an evolution of third-generation mobile telecommunications technology (3G), and is generally referred to as 3.9G. LTE is an international general standard that is based on an orthogonal frequency-division multiple access (OFDMA) technology and is formulated by the 3rd Generation Partnership Project (3GPP) organization, and includes two modes: frequency-division duplexing (FDD) and time-division duplexing (TDD) that are used for paired spectrum and unpaired spectrum. There is only a relatively small difference between FDD and TDD in the LTE standard, and the similarity between the two modes reaches 90%.
LTE to which the FDD mode is applied is FDD-LTE. As a requirement for LTE, evolution of a TDD system is synchronous to evolution of an FDD system.
The FDD mode is characterized in that receiving and transmission are performed in two separated (with an interval of 190 megahertz (MHz) between uplink and downlink frequencies) symmetrical frequency channels.
In an LTE-FDD system, uplink and downlink resources occupy a same bandwidth, but uplink and downlink services are not necessarily symmetrical. If downlink services are more than uplink services, resource waste may be caused. A station with a large demand for downlink services may transmit downlink data by using an idle uplink frequency band, so as to make full use of resources.
However, a total transmit power of a base station is generally higher than a bandwidth occupied by a user equipment (UE), and therefore, if the base station directly sends a downlink signal in the entire uplink frequency band, it may be caused that signal strength leaked from the downlink signal to an adjacent frequency band is higher than an interference tolerance threshold of the adjacent frequency band (as shown in FIG. 1), causing severe interference to communication of a UE in the adjacent frequency band.
In conclusion, at present, when an uplink frequency band is occupied for downlink transmission, severe interference to communication of a UE in an adjacent frequency band may be caused.